Hi, quick question for those in the know as I am also building a workbench with steel top - do you do anything special with it to stop it rusting? Any coating that can be welded on or just an occasional wipe with WD40?
The usual thing to do is to leave the black millscale on, to protect the tabletop - it's hard and will last, as long as it doesn't get damp.
My fab table top had a very thin layer on when i built it though, too thin to protect anything, so we sanded it off, and I use boiled linseed oil. It wipes on like oil, but forms a semi-hard dry coating over the top, but thin enough that you still get electrical conductivity, and it's done me a couple of years now, especially the winter before last where the old workshop was very very damp. I just give it a rub over every few months or so after a decent size job.